The present invention relates to fuel cell stack assemblies and, more particularly, to improved interfacial and edge seals between components of same.
Solid polymer electrolyte fuel cell power plants are known in the art. One example of a polymer membrane power plant is shown in U.S. Pat. No. 5,360,679, issued Nov. 1, 1994.
Known fuel cell constructions commonly include a proton exchange membrane disposed between cathode and anode plates. As is well known to a person of ordinary skill in the art, the operation of a proton exchange membrane (PEM) fuel cell includes the supply of gaseous fuel and an oxidizing gas (oxidant) to the anode electrode and cathode electrode, respectively. The fuel and oxidant is distributed as uniformly as possible over the active surfaces of the respective electrodes, and an electrochemical reaction takes place between the anode and cathode, with attendant formation of a product of the reaction between the fuel and oxygen, release of thermal energy, creation of an electrical potential difference between the electrodes, and travel of electric charge carriers between the electrodes, with the thus generated electric power usually constituting the useful output of the fuel cell.
Another important component of a typical fuel cell stack assembly is a water transport plate, which is a porous structure filled with water during operation of the fuel cell to supply water locally to maintain humdification of the proton exchange membrane, and to remove product water formed at the cathode, among other things.
Along with the water transport plate, the anode and cathode electrode substrates are also porous. With such porous components, it is necessary to insure that neither liquid, such as product or coolant water in a typical fuel cell, nor any gaseous media such as fuel or oxidant, be able to flow in or out of the periphery or edge of the respective porous components. Various attempts have been made in the prior art to provide a seal design for sealing the peripheral edges of these components. Despite these efforts, problems with such sealing remain.
For example, seals within a fuel cell stack assembly typically have bonds, especially to the membrane component, which have weak bond strength to start with, and this bond strength becomes weaker when the cell is subjected to hot water, for example during normal operation of the cell.
Furthermore, provision of good seals between other components, such as between the water transport plates and adjacent anode and cathode substrates, typically require gaskets and the like, which are larger than may be desirable, and which require relatively deep steps to be machined into the water transfer plate assembly, which weakens an already fragile part.
Based upon the foregoing, it is clear that an improved fuel cell stack assembly is desired which is inexpensive and capable of mass production, which will produce a lower cost assembly with improved performance while simplifying assembly. It is particularly preferred to simplify and improve the edge sealing of components of the fuel cell stack assembly, without sacrificing efficient operation of the cell.
Based upon the foregoing, it is the primary object of the present invention to provide a fuel cell stack assembly which has improved interfacial and edge seals.
It is a further object of the present invention to provide such an assembly wherein large gaskets are avoided, and deep steps in water transfer plate components are not needed.
It is a further object of the present invention to provide such an assembly wherein the edge seals can be provided as a single impregnating and seal-forming step such that the sealing material penetrates the cathode and anode substrates, as well as perforations in the membrane, and further forms an outwardly facing bead which provides for an excellent seal with adjacent water transport components.
Other objects and advantages of the present invention will appear hereinbelow.
In accordance with the present invention, a unitized electrode assembly for a fuel cell stack assembly is provided, which comprises a membrane electrode assembly having a first side, a second side, a peripheral edge area and a plurality of perforations along said peripheral edge area; a cathode substrate adjacent to said first side; an anode substrates adjacent to said second side; and a seal material bonding said cathode substrate to said anode substrate and extending through said plurality of perforations.
In addition to the membrane electrode assembly, the anode and cathode substrates can advantageously be provided with perforations, and the seal material injected through perforations of both the membrane and substrates, so as to form an excellent seal between the substrates and further to define a bead on outwardly facing surfaces of the substrates which provides for an excellent seal to adjacent components such as water transport plates and the like.